1. Field of the Invention
The present invention is directed to lubricant base oils/base stocks used to produce formulated lubricants containing performance additives.
2. Description of the Related Art
Hydrocarbon base oils have differing solvency characteristics that affect their capability to solubilize performance additives. Highly paraffinic hydro-carbon base oils (those having low levels of aromaticity) are known to have low-to-poor additive solubility characteristics. For example, such low-solvency hydrocarbon base oils include polyalpha olefins (PAO) which are 100% isoparaffinic and have essentially 0% aromatics content. Similarly, wax isomerate base oils/base stocks, in particular hydroisomerized Fischer-Tropsch (F-T) lubricant fluids, often called Gas-to-Liquids (GTL) lubricant base oils/base stocks, are very highly paraffinic and have essentially 0% aromatics content. Consequently, such wax isomerate base oils would be expected to have low solvency and poor additive solubility performance, and this has in fact been found to be the case.
To address this concern one would expect that the mere addition of an aromatics containing stream to such low solvency base oils/base stocks would uniformly cure the solvency deficiency of such base oils and that such improvement in solvency would be, at best, a linear relationship base on the inherent solvency (expressed as aniline point) of each constituent.
Solvency of lube base oils/base stocks is classically measured by aniline point, and differences in aniline point indicate differences in the solvency capabilities of lube base oils/base stocks and consequently reflect on their capabilities in solubilizing performance additives. Solubility performance increases as aniline point decreases.
Currently, highly paraffinic base oils, such as PAO, are typically used with a co-base oil (e.g., hydrocarbyl oils containing amide, ester, carboxyl, carbonyl, ether, aromatic, or other chemical functionality capable of solvating additives) to provide adequate additives solubility in finished lubricants or functional fluids.
Analogous to PAO, highly paraffinic GTL-type wax-derived base oils would likely be used in combination with hydrocarbyl co-base oils, for example aromatics-containing co-base oils, which may include mineral oils (Group I type). In particular, GTL-type wax-derived base oil/Group I mineral oil combinations could have substantial economic advantages, with the potential for lower cost base oil mixtures which would be useful in formulated lubricant compositions or functional fluids.
The advantage to using a mineral oil as the co-base oil is readily apparent in terms of availability, cost, quality control, quantity, etc.
US 2004/0094453 addresses a process for producing a lube base oil blend which comprises (a) recovering a F-T derived distillate fraction characterized by a kinematic viscosity of about 2 mm2/s or greater but less than 3 mm2/s at 100° C. and (b) blending the aforesaid F-T derived distillate fraction with a petroleum derived base oil selected from the group consisting of a Group I base oil, a Group II base oil, a Group III base oil or a mixture of two or three of any of the aforesaid conventional base oils to produce a blend lubricant base oil having a viscosity of about 3 mm2/s or greater. In the text formulated lubricants comprising F-T derived base oils mixed with 600 neutral and heavy neutral oils are presented. F-T derived base oils having a KV of about 2.5 mm2/s at 100° C. were also combined with bright stock to produce a blended base oil but such a blend was not additized to yield a formulated oil. Only the viscosities, VI, pour point, CCS@−25° C., TGA Noack of such blends are reported.
WO 2004/053030 is directed to functional fluids having low Brookfield viscosity using high viscosity index base oils/base stocks. One such high viscosity index base oil/base stock is identified as Invention Oil B which is described as being made from a F-T wax feedstock. This F-T wax base oil is combined with a comparative base stock in a 50/50 basis and additized. As is clear from Table 4 of WO 2004/053030 the comparative base stock is not bright stock insofar as a formulated lubricant made by adding only 11.379 vol % additive to the comparative base stock produced a blend having a viscosity of only 7.614 mm2/s@100° C., far below what would be expected had the competitive base stock been a bright stock.
U.S. Pat. No. 6,627,779 is directed to blended lube base oils comprising about 99 wt % to about 50 wt % highly paraffinic lube base stock and about 1 wt % to about 50 wt % alkyl aromatics, alkyl cycloparaffins or mixtures thereof. Highly paraffinic base stocks such as F-T derived lube base stocks typically have poor additive solubility. To address this deficiency such base stocks are usually mixed with various co-solvents such as synthetic esters. Synthetic esters are expensive, however, so the resulting blends are also expensive. To overcome this problem U.S. Pat. No. 6,627,779 teaches the addition of from about 1 wt % to about 50 wt % alkyl aromatic, alkyl cycloparaffinis or mixtures thereof to highly paraffinic F-T lube base oils to improve, among other characteristics, the solvency properties of the base oil.